1. Field of the Invention
The present invention relates to a CATV terminal unit, and in particular, to a CATV terminal unit for converting an input radio frequency (RF) signal into a desired channel and for directly supplying an input RF signal to a TV receiver, a VCR, or the like through a external unit connection terminal.
2. Description of the Related Art
As disclosed in, for example, Japanese Patent Laid-Open Publication No. 6-253276, such a CATV terminal unit is used so as to improve and stabilize S/N ratio of input signals of an external unit connection terminal side and an internal tuner side of the CATV terminal unit that has an external unit connection terminal for distributing the output signal to the external unit and the internal tuner.
FIG. 14 is a block diagram showing an example of the structure of a conventional CATV terminal unit.
The CATV terminal unit comprises a variable attenuator 102, a radio frequency amplifier 103, a distributing device 104, an external unit connection terminal 108, a tuner 105, an RF detecting portion 109, and a gain controlling circuit 110. The variable attenuator 102 adjusts the level of a picture signal received from a cable of the CATV system. The radio frequency amplifier 103 amplifies an output signal of the variable attenuator 102. The distributing device 104 distributes an output signal of the radio frequency amplifier 103 to the external unit connection terminal 108 and the tuner 105. The RF detecting portion 109 detects the level of an output signal of the radio frequency amplifier 103. The gain controlling circuit 110 receives an output signal of the RF detecting portion 109 and generates a control signal for controlling the attenuation amount of the variable attenuator 102 so as to control the attenuation amount of the variable attenuator 102.
Next, the operation of the CATV terminal unit shown in FIG. 14 will be described. A cable TV signal is received from a radio frequency (RF) input terminal. The cable TV signal is supplied to the radio frequency amplifier 103 through the variable attenuator 102. The output signal of the radio frequency amplifier 103 is supplied to the distributing device 104. The distributing device 104 distributes the signal received from the radio frequency amplifier 103 to both the tuner 105 and the external connection terminal 108. A VCR or the like can be connected to the external connection terminal 108.
The tuner 105 selects a channel and outputs an intermediate frequency signal. The intermediate frequency signal is supplied to the intermediate frequency amplifying and detecting portion 106. The intermediate frequency amplifying and detecting portion 106 demodulates a picture signal and an audio signal. An output signal of the intermediate frequency amplifying and detecting portion 106 is supplied to a terminal 107. In addition, the intermediate frequency amplifying and detecting portion 106 detects the amplitude of the intermediate frequency signal and so forth, generates an automatic gain control voltage (AGC voltage) and so forth in such a manner the level of the intermediate frequency signal becomes constant, and supplies the AGC voltage to an amplifier of the tuner 105.
In this apparatus, the output signal of the radio frequency amplifier 103 is supplied to the radio frequency detecting portion 109. The radio frequency detecting portion 109 detects for example the average level of the radio frequency signal. The detected output signal of the radio frequency detecting portion 109 is supplied to the gain controlling circuit 110. The gain controlling circuit 110 controls the attenuation amount of the variable attenuator 102 so that the average level is in a predetermined range. Thus, the noise and distortion of the output signal of the distributing device 104 can be stabilized.
A first drawback of the related art reference is in that in the power OFF state of the CATV terminal unit the RF signal received from the input terminal is not supplied to the external unit connection terminal.
In other words, in the power OFF state of the CATV terminal unit, the power is not supplied to the radio frequency amplifier of the CATV terminal unit. Thus, the signal is not supplied to circuits after the radio frequency amplifier.
A second drawback of the related art reference is in that an up signal for bidirectional communication cannot be sent.
In other words, a means for sending the up signal is not provided.